Four common bad habits combined — smoking, drinking too much, inactivity and poor diet — can age you by 12 years, sobering new research suggests.

The findings are from a study that tracked nearly 5,000 British adults for 20 years, and they highlight yet another reason to adopt a healthier lifestyle.

Overall, 314 people studied had all four unhealthy behaviors. Among them, 91 died during the study, or 29 percent. Among the 387 healthiest people with none of the four habits, only 32 died, or about 8 percent.

The risky behaviors were: smoking tobacco; downing more than three alcoholic drinks per day for men and more than two daily for women; getting less than two hours of physical activity per week; and eating fruits and vegetables fewer than three times daily.

These habits combined substantially increased the risk of death and made people who engaged in them seem 12 years older than people in the healthiest group, said lead researcher Elisabeth Kvaavik of the University of Oslo.

The study appears in Monday's Archives of Internal Medicine.

The healthiest group included never-smokers and those who had quit; teetotalers, women who had fewer than two drinks daily and men who had fewer than three; those who got at least two hours of physical activity weekly; and those who ate fruits and vegetables at least three times daily.

"You don't need to be extreme" to be in the healthy category, Kvaavik said. "These behaviors add up, so together it's quite good. It should be possible for most people to manage to do it."

For example, one carrot, one apple and a glass of orange juice would suffice for the fruit and vegetable cutoffs in the study, Kvaavik said, noting that the amounts are pretty modest and less strict than many guidelines.

The U.S. government generally recommends at least 4 cups of fruits or vegetables daily for adults, depending on age and activity level; and about 2 1/2 hours of exercise weekly.

Study participants were 4,886 British adults aged 18 and older, or 44 years old on average. They were randomly selected from participants in a separate nationwide British health survey. Study subjects were asked about various lifestyle habits only once, a potential limitation, but Kvaavik said those habits tend to be fairly stable in adulthood.

Death certificates were checked for the next 20 years. The most common causes of death included heart disease and cancer, both related to unhealthy lifestyles.

Kvaavik said her results are applicable to other westernized nations including the United States.

June Stevens, a University of North Carolina public health researcher, said the results are in line with previous studies that examined the combined effects of health-related habits on longevity.

The findings don't mean that everyone who maintains a healthy lifestyle will live longer than those who don't, but it will increase the odds, Stevens said.